1. Field of the Invention
The present invention relates to an anode for various electrolyses, which is especially desirable as an anode for an electrolytic cell for the manufacture of chlorine-alkali and chloric acid alkali, and for sea water electrolysis, and a manufacturing method thereof.
2. Description of the Related Art
Recently, such cases have been reported as problematic that with the brine electrolytic cell by the ion exchange membrane process, liquefaction cost for enhancing purity of chlorine gas is high and a large amount of hydrochloric acid is added. In view of these, an anode is required which has a specification to evolve by-product oxygen gas at a concentration lower than that by conventional anodes. The reaction process for the evolution of by-product oxygen is as follows:H2O→2H+1/2O2+2e 
As an anode to evolve by-product oxygen gas at a low concentration, a specification applying platinum component is promising. Conventionally, the following anodes for electrolysis by a specification applying platinum component have been reported, which comprises:
an anode having the first coating layer of platinum-iridium oxide mixture, on which the second coating layer by a mixture of 2˜50 mass % of manganese oxide containing non-stoichiometric compound, expressed as MnOx (x being 1.5 or more but less than 2.0) and 50-98 mass % of titanium oxide having a rutile structure is provided (Patent Document 1); an anode having the first coating layer by a mixture of 20˜80 mol. % of platinum and 20˜80 mmol. % of iridium oxide having a rutile structure and the second coating layer by a mixture of 3˜15 mol. % of iridium oxide having a rutile structure, 5˜25 mol. % of ruthenium oxide and 60˜92 mol. % of titanium oxide, these two layers constituting a unit layer, the anode being provided with a single, or a plurality of the unit layer (Patent Document 2); and an anode having the first coating layer by a mixture of 20˜80 mol. % of platinum and 20˜80 mol. % of iridium oxide having a rutile structure and the second coating layer by a mixture of 3˜15 mol. % of iridium oxide having a rutile structure and 5-25 mol. % of ruthenium oxide and 60-92 mmol. % of tin oxide, these two layers constituting a unit layer; the anode being provided with a single, or multiple numbers of the unit layer (Patent Document 3).
However, further improvement is required for these anodes, because they bear such problems with long-time stability as a selective consumption of platinum, passivation or insufficient durability